This invention is generally directed to improvements in CRT (cathode ray tube) manufacture. It is more specifically directed to an improved controller for adjusting the exposure time of a conventional light house on which CRT phosphors are exposed.
In the manufacture of CRTs, a so-called light house supports the faceplate of a CRT and its mask while a light source directs light through apertures in the mask to expose phosphors or other light sensitive materials on the screen of the CRT. The exposure time of the light house is critical and depends, in part, on the size of the apertures in the mask. For this reason, mask manufacturers measure the size of the apertures in each mask and segregate the masks according to aperture size. The exposure time of a light house is then pre-set to accommodate masks having a given aperture size. All masks of that size are then processed on the light house. To process masks of a different size, the exposure time of the light house is changed, and all masks of the new size are then processed.
The difficulty with the procedure described above is that masks must be segregated by size, and that segregation must be maintained. Inadvertent mixing of masks with different aperture sizes invariably produces rejects in the finished product. If the light house could accommodate masks with mixed aperture sizes, CRT production would be more easily accomplished.
Accordingly, it is a general object of the invention to provide an improved method of processing CRT screens and masks on a light house.
It is a more specific object of the invention to provide a method and apparatus for automatically controlling the exposure time of a light house to accommodate masks whose aperture size varies over a substantial range.